In the field of off-highway trucks used, for example, in mining operations, it is desirable that an accurate record be kept of the quantity of material removed from the mining site. This information can be used to calculate mine and truck productivity as well as aid in forecasting profitability and work schedules.
Prior systems, as disclosed in U.S. application Ser. No. 749,607 filed June 25, 1985 by D. Foley et al., have shown that strut pressure can be an accurate indicator of payload. The apparatus disclosed therein includes an electronic control which monitors each of the strut pressures, compensates for various inaccuracies introduced by load distribution and vehicle attitude, and correlates this information into actual payload. However, proper operation of the payload monitor requires that all of the struts be in good working order. For example, theoretical calculations for a particular family of struts have shown that a loss of 125 ml of oil from a single strut can generate a 22% error in calculated payload. No provision has been made for monitoring the condition of the struts and indicating the condition of a faulty strut.
Prior systems have relied upon the vehicle operator to visually inspect each of the struts before operating the vehicle. This practice introduces considerable subjectivity into the system and results in the vehicle being operated with partially or completely collapsed struts. Both operator inattention and inability to recognize a collapsed strut are contributing factors to erroneous operation; however, even with proper inspections the strut may also collapse during operation. In large off-highway trucks, a single collapsed strut will not have significant effect on the "feel" of the truck and can easily go unnoticed by an experienced operator.
Operation of the vehicle with a collapsing strut will have obvious effects on the accuracy of the payload monitor owing to the change in the relationship between strut pressure and payload. Other serious consequences also result from such operation. For example, uneven tire wear is an undesirable result of extended vehicle operation with a collapsed strut. Tires are a major operating expense of off-highway trucks and any change in their replacement schedule can have serious impact on profitability. Thus, a collapsed strut can have economic impact other than replacement of the damaged strut. Moreover, a completely collapsed strut results in repeated metal-to-metal contact and the possibility of eventual major structural failure. Frame damage can occur after relatively short periods of operation and the resultant repair costs can be exorbitant.
The present invention is directed to overcoming one or more of the problems as set forth above.